Field of the Invention
The present invention relates to an exhaust muffler device having two or more expansion chambers into which exhaust gas from a combustion engine flows.
Description of Related Art
An exhaust muffler device having a plurality of expansion chambers has been known in which an exhaust valve is provided to bypass a portion of exhaust gas, from the expansion chamber on the upstream side, to the expansion chamber on the downstream side, in order to protect the exhaust muffler device from high-pressure exhaust gas (for example, JP Laid-open Patent Publication No. 2011-117412).
In the exhaust muffler device described in JP Laid-open Patent Publication No. 2011-117412, when an exhaust valve is opened, exhaust gas that flows in a main passage and exhaust gas that flows in a bypass passage are merged in an expansion chamber on the downstream side, and the merged exhaust gas is discharged to the outside through a discharge pipe. In a case where the discharge pipe has a large diameter, muffling effect or silencing effect may not be sufficient when the exhaust valve is closed. On the other hand, in a case where the discharge pipe has a small diameter, engine output may be reduced when the valve is opened, or internal pressure in the expansion chamber on the downstream side may be excessive when the valve is opened.